For low-complexity operation in a mobile communication system, it has been assumed that the interference signals have a Gaussian distribution. The complexity of implementing communication systems has been lowered by performing operations such as adaptive modulation, adaptive coding, and hard-decision decoding metric generation under this assumption.
In related art techniques, modulation schemes based on quadrature amplitude modulation (QAM) are mainly used to make the distribution of interference signals resemble a Gaussian distribution as much as possible. In this context, QAM symbols may be repeatedly sent to a user to achieve the target performance when a target error performance set for the user is not achieved even after application of the minimum channel coding rate and minimum modulation order.
Communication entities using existing modulation schemes, such as QAM, frequency-shift keying (FSK), and phase-shift keying (PSK), may transmit and receive information by differentiating sizes, frequencies or phases of symbols in the time or spatial domain of signals. When the channel gain is above a preset threshold, various interference levels are low, or a high transmit power is used, as the effective distance between symbols increases at the receiver side, it is possible to increase the data rate by using a high-order modulation scheme.
Meanwhile, in a cellular wireless communication network, there are downlink transmission from a base station to a user equipment and uplink transmission from a user equipment to a base station. Here, for a user equipment performing uplink transmission, the peak-to-average-power ratio (PAPR) is important since battery consumption is to be minimized. In the cellular mobile communication standard such as 3GPP LTE, single carrier frequency division multiple access (SC-FDMA) is applied in the uplink to reduce the PAPR. Hence, it is necessary to develop a modulation method and apparatus that do not cause the high PAPR problem during signal transmission and reception based on not only orthogonal frequency-division multiple access (OFDMA) but also SC-FDMA.